Java中ThreadLocalMap解决Hash冲突的实现方式

static class ThreadLocalMap {

    // 存储条目的数组
    private Entry[] table;
    
    // 存储条目的数量
    private int size = 0;
    
    // 定义初始容量
    private static final int INITIAL_CAPACITY = 16;

    // 构造函数
    ThreadLocalMap(ThreadLocal<?> firstKey, Object firstValue) {
        table = new Entry[INITIAL_CAPACITY];
        int i = firstKey.threadLocalHashCode & (INITIAL_CAPACITY - 1);
        table[i] = new Entry(firstKey, firstValue);
        size = 1;
    }

    // 线性探测法获取 Entry
    private Entry getEntry(ThreadLocal<?> key) {
        int i = key.threadLocalHashCode & (table.length - 1);
        Entry e = table[i];
        if (e != null && e.get() == key)
            return e;
        else
            return getEntryAfterMiss(key, i, e);
    }

    // 线性探测法后处理
    private Entry getEntryAfterMiss(ThreadLocal<?> key, int i, Entry e) {
        Entry[] tab = table;
        int len = tab.length;

        while (e != null) {
            ThreadLocal<?> k = e.get();
            if (k == key)
                return e;
            if (k == null)
                expungeStaleEntry(i);
            else
                i = nextIndex(i, len);
            e = tab[i];
        }
        return null;
    }

    // 设置值
    private void set(ThreadLocal<?> key, Object value) {
        Entry[] tab = table;
        int len = tab.length;
        int i = key.threadLocalHashCode & (len - 1);

        for (Entry e = tab[i]; e != null; e = tab[i = nextIndex(i, len)]) {
            ThreadLocal<?> k = e.get();

            if (k == key) {
                e.value = value;
                return;
            }

            if (k == null) {
                replaceStaleEntry(key, value, i);
                return;
            }
        }

        tab[i] = new Entry(key, value);
        int sz = ++size;
        if (!cleanSomeSlots(i, sz) && sz >= threshold)
            rehash();
    }

    // 获取下一个索引
    private int nextIndex(int i, int len) {
        return ((i + 1 < len) ? i + 1 : 0);
    }

    // 替换过时条目
    private void replaceStaleEntry(ThreadLocal<?> key, Object value, int staleSlot) {
        Entry[] tab = table;
        int len = tab.length;
        Entry e;

        int slotToExpunge = staleSlot;
        for (int i = prevIndex(staleSlot, len);
             (e = tab[i]) != null;
             i = prevIndex(i, len)) {
            if (e.get() == null)
                slotToExpunge = i;
        }

        for (int i = nextIndex(staleSlot, len);
             (e = tab[i]) != null;
             i = nextIndex(i, len)) {
            ThreadLocal<?> k = e.get();

            if (k == key) {
                e.value = value;

                tab[i] = tab[staleSlot];
                tab[staleSlot] = e;

                if (slotToExpunge == staleSlot)
                    slotToExpunge = i;
                cleanSomeSlots(expungeStaleEntry(slotToExpunge), len);
                return;
            }

            if (k == null && slotToExpunge == staleSlot)
                slotToExpunge = i;
        }

        tab[staleSlot].value = null;
        tab[staleSlot] = new Entry(key, value);

        if (slotToExpunge != staleSlot)
            cleanSomeSlots(expungeStaleEntry(slotToExpunge), len);
    }

    // 处理过时条目
    private int expungeStaleEntry(int staleSlot) {
        Entry[] tab = table;
        int len = tab.length;

        tab[staleSlot].value = null;
        tab[staleSlot] = null;
        size--;

        Entry e;
        int i;
        for (i = nextIndex(staleSlot, len);
             (e = tab[i]) != null;
             i = nextIndex(i, len)) {
            if (e.get() == null) {
                e.value = null;
                tab[i] = null;
                size--;
            } else {
                int h = e.get().threadLocalHashCode & (len - 1);
                if (h != i) {
                    tab[i] = null;

                    while (tab[h] != null)
                        h = nextIndex(h, len);
                    tab[h] = e;
                }
            }
        }
        return i;
    }

    // 清理某些槽位
    private boolean cleanSomeSlots(int i, int n) {
        boolean removed = false;
        Entry[] tab = table;
        int len = tab.length;
        do {
            i = nextIndex(i, len);
            Entry e = tab[i];
            if (e != null && e.get() == null) {
                n = len;
                removed = true;
                i = expungeStaleEntry(i);
            }
        } while ((n >>>= 1) != 0);
        return removed;
    }

    // 重新哈希
    private void rehash() {
        expungeStaleEntries();

        if (size >= threshold - threshold / 4)
            resize();
    }

    private void expungeStaleEntries() {
        Entry[] tab = table;
        int len = tab.length;
        for (int j = 0; j < len; j++) {
            Entry e = tab[j];
            if (e != null && e.get() == null)
                expungeStaleEntry(j);
        }
    }

    private void resize() {
        Entry[] oldTab = table;
        int oldLen = oldTab.length;
        int newLen = oldLen * 2;
        Entry[] newTab = new Entry[newLen];
        int count = 0;

        for (int j = 0; j < oldLen; ++j) {
            Entry e = oldTab[j];
            if (e != null) {
                ThreadLocal<?> k = e.get();
                if (k == null) {
                    e.value = null;
                } else {
                    int h = k.threadLocalHashCode & (newLen - 1);
                    while (newTab[h] != null)
                        h = nextIndex(h, newLen);
                    newTab[h] = e;
                    count++;
                }
            }
        }

        setThreshold(newLen);
        size = count;
        table = newTab;
    }
}